﻿/* 
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;

using PriorityQueueExtension = Lucene.Net.Util.PriorityQueueExtension;

namespace Lucene.Net.Search
{

    public sealed class HitQueueExtension : PriorityQueueExtension
    {

        private bool prePopulate;

        /// <summary> Creates a new instance with <code>size</code> elements. If
        /// <code>prePopulate</code> is set to true, the queue will pre-populate itself
        /// with sentinel objects and set its {@link #Size()} to <code>size</code>. In
        /// that case, you should not rely on {@link #Size()} to get the number of
        /// actual elements that were added to the queue, but keep track yourself.<br/>
        /// <b>NOTE:</b> in case <code>prePopulate</code> is true, you should pop
        /// elements from the queue using the following code example:
        /// 
        /// <pre>
        /// PriorityQueue pq = new HitQueueExtension(10, true); // pre-populate.
        /// ScoreDoc top = pq.top();
        /// 
        /// // Add/Update one element.
        /// top.score = 1.0f;
        /// top.doc = 0;
        /// top = (ScoreDoc) pq.updateTop();
        /// int totalHits = 1;
        /// 
        /// // Now pop only the elements that were *truly* inserted.
        /// // First, pop all the sentinel elements (there are pq.size() - totalHits).
        /// for (int i = pq.size() - totalHits; i &gt; 0; i--) pq.pop();
        /// 
        /// // Now pop the truly added elements.
        /// ScoreDoc[] results = new ScoreDoc[totalHits];
        /// for (int i = totalHits - 1; i &gt;= 0; i--) {
        /// results[i] = (ScoreDoc) pq.pop();
        /// }
        /// </pre>
        /// 
        /// <p/><b>NOTE</b>: This class pre-allocate a full array of
        /// length <code>size</code>.
        /// 
        /// </summary>
        /// <param name="size">the requested size of this queue.
        /// </param>
        /// <param name="prePopulate">specifies whether to pre-populate the queue with sentinel values.
        /// </param>
        /// <seealso cref="GetSentinelObject()">
        /// </seealso>
        public /*internal*/ HitQueueExtension(int size, bool prePopulate)
        {
            this.prePopulate = prePopulate;
            Initialize(size);
        }

        // Returns null if prePopulate is false.
        protected internal override System.Object GetSentinelObject()
        {
            // Always set the doc Id to MAX_VALUE so that it won't be favored by
            // lessThan. This generally should not happen since if score is not NEG_INF,
            // TopScoreDocCollector will always add the object to the queue.
            return !prePopulate ? null : new ScoreDoc(System.Int32.MaxValue, System.Single.NegativeInfinity);
        }

        public override bool LessThan(System.Object a, System.Object b)
        {
            ScoreDoc hitA = (ScoreDoc)a;
            ScoreDoc hitB = (ScoreDoc)b;
            if (hitA.score == hitB.score)
                return hitA.doc > hitB.doc;
            else
                return hitA.score < hitB.score;
        }
    }
}